1. Field of the Invention
This invention relates to energy-absorbing bolsters for automotive instrument panel assemblies.
2. Background Art
An instrument panel (i.e., IP), also called crash pad or dashboard, is an interior part of an automobile that is located below the windshield. An instrument panel accommodates components providing driver and passengers with various information for safe driving, and convenience. The instrument panel integrates meters including speedometer and fuel meter as well as convenience devices such as air bag controls, glove box and radio. Many instrument panel assemblies have plastic components. Factors to be taken account when selecting plastic materials are heat resistance, impact resistance, processability, and dimensional stability. Poor heat resistance might cause the IP to sag by itself and the poor dimensional stability might cause a bad installation or generate noises and vibrations with other side parts.
The lower portions of such instrument panel structures serve as occupant knee and ankle restraints, commonly referred to as “knee bolsters”, to absorb the impact shock of knees and ankles which occurs upon sudden deceleration of the vehicle caused by a collision or high level braking.
U.S. Pat. No. 5,326,130 discloses a vehicle instrument panel structure for extending transversely across the width of a vehicle interior forwardly of a vehicle occupant seat. The instrument panel structure includes an upstanding backing plate having a layer of foam material thereon covered by a decorative covering. The backing plate is a unitary member formed of a plastic material. A pair of spaced-apart elongated horizontally extending box-like protuberances are provided on one portion of the lower section of the backing plate in the path of occupant knee travel which may occur during sudden deceleration of the vehicle.
U.S. Pat. No. 5,431,442 discloses a passenger restraint structure for an automotive vehicle having a glove box which has at least one face that is able to be opened to a passenger compartment and is attached to an instrument panel so as to be opposed to the knees of a passenger. The glove box has an intermediate wall connecting a front wall and a rear wall of the glove box. A stiffener member is located between the glove box and a part of a vehicle body and is stiffer than the glove box for crash energy generated between the passenger and the vehicle body in the running direction of the vehicle. Upon impact, the weaker intermediate wall of the glove box is compressed, deformed and broken, thereby absorbing the crash energy.
U.S. Pat. No. 5,311,960 discloses a multifunctional structural cross vehicular beam assembly extending across substantially the entire width of the vehicular compartment between a cowl and a instrument panel. The beam supports the steering column of the vehicle so that the first bending mode frequency of the combination of the steering wheel and the beam is greater than the first bending mode frequency of the body and is different from the idle excitation frequency of an engine employed in the vehicle. A plastic cover is connected to the beam for defining channels of an air distribution system for the passenger compartment.
U.S. Pat. No. 6,199,942 discloses an energy-absorbing assembly for decelerating an object that impacts the assembly. The assembly comprises at least one energy-absorbing member for accommodating deformation of the assembly. The assembly comprises a base and at least one energy-absorbing module associated therewith. The at least one energy-absorbing module is formed from a group consisting of structure (A) and structure (B). Structure (A) is a metal lattice which is supported by the thermoformed base. Structure (B) comprises of a plurality of recesses, each having a floor and a wall. Together, structures (A) and (B) and combinations thereof afford a user-determinable resistance to impact.
U.S. Pat. No. 6,474,687 discloses a one-piece knee bolster for a motor vehicle including a knee bolster cover adapted to mount to a vehicle structure in an interior of a motor vehicle and at least one hollow reinforcing channel member extending along the knee bolster cover to reinforce the knee bolster cover.
U.S. Pat. No. 6,464,255 discloses a knee bolster airbag system to dissipate impact energy during an impact of a vehicle in which the system is disposed. The system includes a base which has a first surface disposed toward a vehicle compartment of the vehicle, and a cover having an inner surface attached adjacent the first surface of the base to define a cavity. The cover further has opposite first and second edges, wherein the first edge pivotally attaches the cover to the base about an axis to hinge the first edge of the cover to the base. The system further includes an airbag housing member adjacent which an airbag and a gas source are disposed. The system further includes a tether connected to the base and the cover. The tether allows a predetermined displacement of the second edge away from the base when the airbag is in a deployed state.
U.S. Pat. No. 6,869,123 discloses an instrument panel assembly including an elongate beam structure and a plurality of thermoplastic energy absorbers coupled to the beam structure. The instrument panel assembly also includes at least one knee bolster positioned adjacent the plurality of thermoplastic energy absorbers and an instrument panel.
U.S. Pat. No. 6,797,089 discloses an energy management system having a substrate and a crash pad that are vibration welded together. A method for vibration welding first and second parts made of materials that are incompatible with being vibration welded includes prior to vibration welding the first and second parts, adhering to a surface of at least the first part of a layer of material that is compatible with being vibration welded to the second part.
In the manufacture of vehicles, such as passenger cars and trucks, there are many safety standards that must be met by the vehicles to reduce the likelihood and/or severity of injury to occupants during an accident. For example, in the United States the safety standard FMVSS 208 deals with the risk of knee injury arising from contacting the vehicle instrument panel during a frontal crash. In order to meet the safety standard, portions of an instrument panel assembly are required to absorb at least some of the energy of an impact by the knees of the front seat occupants during a crash. A portion of the instrument panel that is configured to sustain an impact from the knees of a front seat occupant during a crash is called a bolster. This is the portion of the instrument panel below the belt line.
Government tests are conducted on vehicles to determine if they meet the safety standard, based on the statistically median-sized male occupant. The median size is a statistically determined size whereby 50 percent of the population is larger and 50 percent of the population is smaller.
In some vehicles, the problem of meeting this safety standard is complicated by the fact that the vehicle's glove box is positioned in the same area that is expected to be impacted by the knees of the median-sized passenger during a crash.
The glove box door is typically made from a polymeric material and is injection molded. The injection molding process can itself negatively affect the strength of the plastic material. Thus, the glove box door is typically not considered to be capable of sustaining a substantial portion of the load that results from an impact by the passenger's knees during a crash. Although injection molded pieces have good appearance characteristics, they do not usually have much strength and thus require additional strengthening such as metal plates or wide contact areas with brackets.
U.S. Patent Application Publication No. 2005/0052011 discloses an instrument panel subassembly for use in an instrument panel assembly in a motor vehicle. The subassembly includes first and second generally C-shaped energy absorption brackets. The brackets have an aft facing C-section and upper and lower mounting ends. The brackets include an attachment mechanism for attaching the brackets to a vehicle structural member. The subassembly further includes a glove box door having an aft surface and a forward surface, and a bin. The glove box door includes a hinge mechanism for providing hinged movement of the glove box door relative to the first and second brackets between open and closed positions. The bin is within the C-section of the brackets when the glove box door is in a hingedly closed position.
Vehicle safety standards also require special design parameters relating to the steering column of the vehicle. The steering column must be designed to move in an axial direction if the chest of the driver contacts the steering wheel in the course of a crash. Most steering columns are designed to collapse in an axial direction and the steering column is located and designed with the collapsing structure being calculated on the basis that the steering column is not impacted by other structures within the vehicle. A further aspect of the impact safety design of the vehicle is that the driver's knees will contact the bolster area with one knee on either lateral side of the axis of the steering column. As the driver's knees contact the bolster area, the bolster may bend about a generally vertical plane. Bending of the bolster about a vertical plane may then result in some of the instrument panel structure, including the bolster itself, infringing on the space envelope allowed for the steering column structure. If there is any contact of this surrounding structure with the steering column, then the collapse characteristics of the steering column, in accordance with its design, will be changed due to contact from surrounding structure.
In order to deal with this problem, it is routine in automotive design to include a relatively strong structure, typically a metallic plate, which is attached to the instrument panel structure and which surrounds the steering column envelope. The metal plate may be attached to the bolster or to underlying instrument panel structure. The meal plate is more properly called a steering column protector and is sometimes referred to colloquially as a knee splitter. The function of the structure is to keep the driver's knees spread apart so that neither the knees, the bolster nor any other surrounding structure infringes on the steering column envelope. This ensures that the steering column can collapse in accordance with its designed function.
Most vehicles today have structure built in to help absorb the energy generated by the impact of the driver's knees on the bolster. Typically, most vehicles have energy absorption brackets mounted laterally to either side of the steering column axis outside the steering column envelope. Energy is dissipated as the driver's knees contact the bolster pushing the bolster against the energy absorption brackets and some energy is dissipated by the energy absorption bracket. The energy absorption brackets are located to provide protection to the median sized person as constrained by the vehicle geometry.
In the existing design envelope, bolsters applied to the steering wheel area of cars are relatively complicated structures comprising a bolster as well as the steering column protector. The bolster generally is a surface of the instrument panel that would otherwise be available for viewing by a vehicle occupant and thus the bolster area must meet certain appearance characteristics. Heretofore, bolsters have been made from injection-molded parts, which have good appearance characteristics on the surface which is visible within the vehicle. However, due to the very nature of injection molding, parts made by the injection molding process often have less strength that might otherwise be available from the plastic resins used in the injection molding process. In such designs, an injection-molded bolster is created which has suitable appearance characteristics and the bolster is strengthened by a metallic plate. The steering column protector serves the function of protecting the steering column with the assumption that the driver's knees will be located substantially directly aft of the energy absorption brackets.
While this is a complicated and expensive structure to manufacture, there is also the question of what happens if the driver's knees are not located directly aft of the energy absorption structure. This may be as a result of the driver not meeting the 50 percentile adult male physical-size and the drivers seating position may locate the knees at some point other than directly aft of the energy absorption brackets.
U.S. Patent Application Publication 2005/0052010 discloses a bolster for assembly to an instrument panel assembly of an automotive vehicle. The vehicle has a steering column with a steering column axis and at least two energy-absorbing brackets located laterally to either side of the steering column axis. The bolster comprises a unitary structure having a generally forward wall and a generally aft wall. The forward wall has a forward wall, forward surface. The forward wall, forward surface includes first and second bolster transfer surfaces for transferring forces from the bolster to the energy-absorbing brackets. The bolster further comprises a plurality of generally laterally extending rib structures. The rib structures extend from adjacent the first bolster transfer surface to adjacent the second bolster transfer surface. The plurality of generally laterally extending ribs structures have sufficient strength to inhibit bending of the bolster about a vertical plane when struck by a driver's knees at a point or points that are not directly aft of the bolster transfer surfaces, when the force is equal to or less than an amount specified by a test standard.
One problem associated with most, if not all of the above-noted structures, is that these structures have relatively large mass, complexity and high cost.